The present invention relates to outside plant communications trunk switching apparatus and methods. More particularly, the present invention relates to methods and apparatus for selectively switching remotely located pairs of one trunk to one or the other corresponding pairs of two available trunks from a central control location.
Communications companies, particularly telephone utility companies, are rapidly decentralizing switching operations from single location central offices located in the heart of dense population centers to locations closer to subscribers. One reason for this decentralization is the increased reliability of central office electronic switching systems which are capable of reliable operation with very little maintenance or attention. Another reason for decentralization is the size, numbers and cost of the cable pair runs from distant subscribers to a central location. It is more economical to collect the cable pairs at a remotely controlled satellite central office close to the subscribers than it is to feed all of the wire pairs to a single distant location.
A need has arisen to provide an effective way for switching pairs of a telephone trunk from one central office to another central office incident to the decentralization of communications switching systems. Heretofore, one approach has been to provide a hard-wired, manual cross-connect system, such as the 3M MS2 Modular Hardwire System offered by 3M Company, Minneapolis, Minn. The drawbacks of such a system are that a cable splicer technician has been required to install and check the jumpers every time a switch has been made. This has required that the technician drive to the remote cross-connect site, enter the housing for the terminal blocks, identify the terminals to be cross-connected, make the cross connections, and then check the connections with technicians located at the terminal ends of the trunks to be sure that the intended cross-connect has been made. This manual procedure was very time consuming and very expensive.
One other procedure followed was to splice loading coils into the trunk and bridge the two trunks together. The loading coils were then removed when the old trunk was disconnected. That approach had the drawback of interjecting a degree of unreliability into the communications paths as the manual splicing work took place.
Thus, a need has arisen for an automatic switch system to switch pairs reliably from one trunk to another trunk to facilitate cut over to new satellite central offices.
A separate, heretofore unfulfilled need has arisen for a remotely controlled switch system which can be centrally operated to switch communications pairs between trunks extending to separate buildings or locations within a single subscriber communications system, as with a company having several buildings or separate operating locations which are interconnected to a single switchboard. Such a system would facilitate switching from the single switchboard to enable employees to move easily from building to building without interruption of telephone service.
Yet another need has arisen for a remotely operated switching system within a subscriber's multiple line telephone system which adds to it the capability to select communications paths from a plurality of pairs in excess of system capacity, so that telephone outlets in excess of the subscriber's needs may be installed to provide the subscriber with flexibility in the placement of its personnel within its facilities.
One more need has arisen for a remotely controlled cable switching system which will maintain a set switch matrix state without power, which derives all of its operating power from a control path from the central control point during a switching or testing sequence, but not otherwise, and which uses commonly available multi-tone bursts (e.g. touch tones) to provide switching commands.
Remotely controlled central office main distribution frame automatic switching systems have been proposed in the prior art. One representative example of a central office switch system is found in the Amos E. Joel, Jr., U.S. Pat. No. 3,562,435, assigned to Bell Telephone Laboratories, Inc. Therein, a constantly powered automatic switch matrix was proposed to connect one side of the main frame to the other side, i.e. outside cable pairs from subscribers to inside plant switching and call handling equipment. That system was very complex and provided true matrix switching, as is required for main frame distribution connections. While a teletypewriter was described as a preferred input-output device, it did not employ multi-burst tones to effectuate switching changes. Moreover, the complex switching apparatus required constant power from the central office power supply in order to maintain its matrix state. Thus, the complex cumbersome switching apparatus proposed by the Joel, Jr., patent did not suggest a solution to the needs identified hereinabove.
Other references known to applicants include the Hjortendal et al. U.S. Pat. No. 3,993,871 which described a reed relay matrix arranged as a cross-connect, but with the requirement of a constant current holding circuit to maintain matrix state. The Kapel et al. U.S. Pat. No. 3,763,325 described a manually operated patch-cord panel for cross-connect. Such system would not be suitable for outside plant locations subjected to the elements, and it suffers from the same drawbacks in requiring an onsite technician as does the manual 3M cross-connect system. The Ueda et al. U.S. Pat. No. 4,079,207 describes a central office switching system including concentration circuits and line hunting functions implemented with plural switch matrixes. The Mehaffey et al. U.S. Pat. No. 4,028,498 is illustrative of a PABX system which includes a cross-connect switch matrix. The switching points are controlled and monitored by a computer. The Anderson U.S. Pat. No. 4,153,943 is illustrative of cross-point switching within a main frame computer memory bank. It shows a serially addressed connection location scheme. While these reference are pertinent to establish the state of the art, they do not singly, or in combination, teach or suggest the present invention.